A display device which makes a displayed video stereoscopically perceived alternately displays a left frame image (referred to as L frame image hereinafter) which is viewed by the left eye and a right frame image (referred to as R frame image hereinafter) which is viewed by the right eye, at predetermined intervals (e.g., field intervals). The displayed L and R frame images have contents different from each other by an amount of parallax. A viewer views the L and R frame images through an eyeglass device which has liquid crystal shutters driven in sync with display periods of the L and R frame images (c.f., JP S62-133891 A and JP 2009-25436 A). Thus, the viewer stereoscopically perceives objects rendered in the L and R frame images.
FIG. 32 is a block diagram showing a conventional video viewing system. The video viewing system depicted in FIG. 32 receives video signals (a left video signal and a right video signal) of 60 Hz.
The video viewing system 900 includes a video signal processor 901 which receives the video signal (the left and right video signals) of 60 Hz. The video signal processor 901 converts the input video signal into the left video signal and the right video signal of 120 Hz. The converted left and right video signals are output to a liquid crystal driver 902 and a backlight controller 903. The liquid crystal driver 902 converts the left and right video signals of 120 Hz into a video display format of a liquid crystal panel 904. The left and right video signals obtained through the conversion by the liquid crystal driver 902 are output to the liquid crystal panel 904. The backlight controller 903 outputs an emission control signal to a backlight source 905. The backlight source 905 irradiates light onto the liquid crystal panel 904 in response to the emission control signal (i.e., the backlight source 905 irradiates the back surface of the liquid crystal panel 904 with light). Thus, the L and R frame images are alternately displayed on the liquid crystal panel 904 at 120 Hz.
The eyeglass device 950 has a left shutter 951 and a right shutter 952. In response to the left and right video signals of 120 Hz obtained through the conversion by the video signal processor 901, a shutter control circuit 906 for the left shutter 951 and a shutter control circuit 907 for the right shutter 952 control the left and right shutters 951, 952 in sync with the left and right video signals.
FIG. 33 is a control timing chart of the conventional video viewing system 900. In FIG. 33, the section (A) shows scanning timings for the L and R frame images of the liquid crystal panel 904. The section (B) of FIG. 33 shows a lighting timing of the backlight source 905. The section (C) of FIG. 33 shows opening and closing timings of the shutters 951, 952 of the eyeglass device 950. The conventional video viewing system 900 is described with reference to FIGS. 32 and 33.
The left and right video signals are sequentially written into the liquid crystal panel 904. Meanwhile, the backlight source 905 is always on. The shutter control circuits 906, 907 control the shutters 951, 952. After the liquid crystal panel 904 is scanned so that the left and right video signals are alternately written into the liquid crystal panel 904, the shutters 951, 952 are opened and closed under the control of the shutter control circuits 906, 907 so that an open period of each shutter becomes the half of each video period. The L and R frame images are viewed by the left and right eyes of the viewer through the shutters 951, 952, respectively. As a result, the viewer creates optical stereoscopic images in the brain.
In the video viewing system which operates at the control timings shown in FIG. 33, the viewer views the L or R frame image only while the shutter 951, 952 is open (for a period long enough to view a video required for the creation of the stereoscopic images). Meanwhile, even in a period other than the period while the shutter 951, 952 is open, the backlight source 905 is always on. Therefore, the video viewing system which operates at the control timings shown in FIG. 33 is not preferable in terms of electric power saving.
FIG. 34 is another control timing chart for the conventional video viewing system 900. In FIG. 34, the section (A) shows scanning timings of the liquid crystal panel 904 for the L and R frame images. The section (B) of FIG. 34 shows a lighting timing of the backlight source 905. The section (C) of FIG. 34 shows opening and closing timings of the shutters 951, 952 of the eyeglass device 950. The conventional video viewing system 900 is further described with reference to FIGS. 32 to 34.
JP 2009-25436 A discloses control under which the backlight source 905 is on only while the L or R frame image is viewed. Unlike the control shown in FIG. 33, the backlight source 905 in the control depicted in FIG. 34 emits light only while the L or R frame image is viewed. Therefore, the control shown in FIG. 34 is superior to the control depicted in FIG. 33 in terms of the electric power saving.
The left shutter 951 is open after the liquid crystal panel 904 displays an L frame image, which is viewed by the left eye, and before the scanning operation of the right video signal for displaying the R frame image. Likewise, the right shutter 952 is open after the liquid crystal panel 904 displays the R frame image, which is viewed by the right eye, and before the scanning operation of the left video signal for displaying the L frame image.
As shown in FIGS. 33 and 34, the scanning operation of the left and/or right video signals starts from an upper portion of the liquid crystal panel 904. Thus, the scanning operation of the left and/or right video signals at a lower portion of the liquid crystal panel 904 happens after the scanning operation of the left and/or right video signals at the upper portion of the liquid crystal panel 904.
It depends on a type of a displayed video how long it takes for a liquid crystal to respond to the left and/or right video signals. For example, if there is a difference in luminance of a pixel between a preceding frame image and a subsequent frame image, it takes relatively long for the liquid crystal to respond.
If the left or right shutter 951, 952 waits for completion of L or R frame image display to open, there may be a shorter time for an open orientation of the left or right shutter 951, 952 because of the long response time of the liquid crystal. As a result, the viewer perceives dark stereoscopic images displayed on the liquid crystal panel 904.
Unless the left shutter 951 waits for the completion of the L frame image display to open, the viewer views the L frame image which is influenced and mixed by the preceding R frame image display. Likewise, if the right shutter 952 opens without waiting for the completion of the R frame image display, the viewer views the R frame image influenced and mixed by the preceding L frame image display. Such mixture between the L and R frame images is called crosstalk. A mixed amount of the preceding frame image (the L or R frame image) increases, in particular, at a lower position of the liquid crystal panel 904 because of the delayed scanning operation of the left and/or right video signal at the lower portion of the liquid crystal panel 904 and the response time of the liquid crystal. Therefore, it is difficult for the viewer to stereoscopically perceive the frame images displayed at the lower portion of the liquid crystal panel 904.
The aforementioned crosstalk problem becomes noticeable, in particular, in stereoscopic video display in which the L and R frame images rendering different contents from each other by the parallax amount are alternately displayed, although the crosstalk problem is a common problem to two-dimensional videos. If there is a large difference in luminance between the preceding and subsequent frame images in an area, it is likely that the viewer perceives the crosstalk. In particular, if the area where there is the large difference in luminance is scanned at a relatively late timing, it becomes more likely that the viewer perceives the crosstalk.